This invention relates generally to a method and apparatus for swaging the end of tubular workpieces, such as drill pipe used in oil and gas well drilling and, particularly to a method of swaging the flared end of a tubular member back to its original size and to a swaging tool having a series of rollers rotatably and axially movable within a mandrel sleeve with a tapered internal surface.
The external surfaces of cylindrical metallic workpieces have been processed by forceably engaging the surface of the workpiece with a circular assembly of rollers during relative rotational movement between the workpiece and the assembly of rollers. Where the workpiece is reduced between 0.0005 and 0.015 of an inch, the tool is considered a burnishing tool, where the reduction in size is greater than 0.015 of an inch in the diameter of the workpiece, the tool is considered a swaging tool. Tools of this type are shown in U.S. Pat. No. 3,815,397, issued June 11, 1974, in the name of Eugene A. Hollencamp. In the Hollencamp patent, the outside diameter of a tubular workpiece is reduced by swaging the workpiece with a short conical portion of a series of rollers and finishing the surface with a longer tapered surface of the roller. The final size of the workpiece is determined by adjusting the mandrel cage and locking the mandrel in position. The rollers which reduce the diameter of the workpiece are then held in a position whereby their surfaces will remain axially stationary while the leading surface will engage the workpiece for the swaging operation and the trailing surface will finish or burnish the surface. Because the rollers remain axially stationary, the degree of size reduction is limited. In the present invention, the leading conical surface of the rollers merely guides the workpiece into the roller cage and the long trailing conical surface performs the swaging operation. In addition, the rollers which effect the size reduction in the O.D. of the workpiece are allowed to move axially within a mandrel sleeve. As the rollers move axially inward of the mandrel sleeve, the diameter of the workpiece surface is continually reduced. The desired final O.D. size of the workpiece is determined by setting stops within the tool, limiting the axial movement of the rollers. By this method, a greater size reduction of the workpiece may be accomplished with one setting of the tool